Electric hotplate and method of making same



Jm, Z4, 957 K. FISCHER ELECTRIC HOTPLATE AND METHOD OF MAKING SAME FiledApril 22, 1964 Kid United States Patent O 3,300,621 ELECTRIC HOTPLATEAND METHOD v F MAKING SAMFJ Karl Fischer, Am Gansherg 1, Gherderdingen-Wurttemberg, Germany Filed Apr. 22, 1964, Ser. No. 361,644 6 Claims.V(Cl. 219-457) This invention relates to electric hotplates and particularly to electric hotplates having grooves on thev underside of theplate body, which are adapted to receive Wire coil heating elementsembedded in insulating compound material, and to methods of making same.

Conventionally known electric hotplates are the kind referred to havingheating elements equipped with comparatively long cable ends passingthrough the insulating compound into which the heating elements areembedded. Outside the insulation, the cable ends usually pass throughanother insulating member which is fitted into the cover shellunderneath the hotplate. The free ends of the cables projecting over thelatter insulating member are protected by covering same with insulatingheatproof glassbeads or the like, and are either connected to a terminalbar mounted below the hotplate assembly, or are arranged as freeconnecting ends onto which further extensions are attached by solderingor welding.

The long flexible cable ends of the heating elements have been foundextremely cumbersome during the manufacturing of the hotplate. Theystart to give rise to diiculties during the placing of the heatingelements into the grooves of the plate where a first layer of insulatingmaterial had been pressed. The heating elements then may be forced outof their seat during the transportation of the hotplates to the nextfollowing manufacturing step due to movements of the connecting ends.Furthermore, the presence of the long free ends of the cable ends alsoare undesirable when the heating elements are covered with the nalinsulating compound to be pressed into the grooves, particularly byobstructing the smoothing of the loosely poured insulating compoundmaterial. The long free hanging connecting ends must be laboriouslythreaded through bores lof the heavy die press head for the subsequentpressing-in of the loose insulating compound into the grooves of thehotplate. Furthermore, these ends are in the way during the subsequentprocessing stages, such as drying, testing and machining. Eventuallythere is the danger that the heating elements may be torn out of theirembedding material by accident or by careless handling after the finalpressing.

According to the present invention, which consists in such novelfeatures, construction arrangements, combinations of parts andimprovements as may be shown and described in connection with theapparatus herein disclosed by way of example only and as illustrative ofa preferred example, the heating elements are equipped with relativelyrigid connecting ends, which ends are dimensioned in such manner thatthey are covered entirely by the loosely poured insulating compoundmaterial. There are several possibilities of rendering the connectingends of the heating elements accessible for connecting after the nalpressing of the insulating material. It is, for example, possible toprovide for connecting ends which are bent-off at a right angle, so thatthey protrude over the insulating material, ready for connecting, byhaving entering of same into frontside clearances in the press dieduring the pressing operation of the insulating material. Furthermore,the. connecting ends could be shaped in such manner that they wouldremain within the confinement of the insulating material after thepressing of the insulating material. In this case, the connecting endsmust be rendered accessible for the connecting by subsequent ICCmachining of small grooves in the compressed insulating material. Itcould be also feasible to insert a low-temperature melting plug on thecorresponding places.

The above-mentioned problems are being eliminated by this. The short,rigid connecting parts, preferably consisting of pins which are of lightweight and constitute only a small lever arm in the bent-off design, do`not iniiuen'ce during transportation the heating `element which islooselyV positioned in the grooves. Since they are entirely'coveredwithin the insulating compound material after this material has beenpoured on over the grooves, they will not be in the way whenthismaterial is smoothed fiat. If the connecting ends are bent oli and ifthey are dimensioned in such manner that they protrude over the linallypressed insulating material, they can enter without diliiculties intocut-outs provided on the pressing die at the time of compressing of theinsulating material. Since the connecting ends only protrude verylittle, for example 7 mm., over the insulating material, they are notobstructing during the subsequent manufacturing operations. There alsois no hazard of ripping out of the heating elements of finally pressedinsulating material by careless handling. The hotplates can be packedand stacked in a space-saving manner, similarly to the plate blanks, fortransporting of same to other manufacturing departments or to theassembly lines, since the connecting parts which only protrude littleover the insulating material, are protected by the higher peripheralborder of the hotplate body. Conductor pieces can be soldered or weldedonto the connecting ends which protrude over the insulating material -orwhich have been rendered accessible by machining of grooves in thismaterial. These conductor pieces are laid out to the outside of thehotplate assembly leading through the insulating member in the covershell underneath the hotplate for being connected to the power lines, asin the case with the conventionally known long cable ends.

There is a further considerably advantage of this structure for themanufacturing of the hotplates. Since the connecting parts are joinedimmediately to the last coils of the heating element, so that it is nolonger necessary for the heating elements having long uncoiled, strandedends, the heating element coils can be cut off currently of acontinuously produced endless spiralling coil emenating from a coilingmachine in increments of suitable length. Thus, these heating elementsmay be produced fully automatically.

The connecting parts of the heating elements are preferably made ofpins. As it is known from tubular heating elements, the connecting partsmay be made of solid metal pins which are pushed into the coils and arewelded or soldered thereto. In a yet more simple manner, the connectingpins may be made of small tubes which are pushed over the short,extended ends of the heating element coils and which are squeezed on tosame for forming a rm joint or of sheet metal strips which are rolledabout the extended ends of the heating element coils and are pressedthereon. The necessary straightening of short lengths of the ends of theheating element coils (approximately 10 to 15 mm.) is compensated byeliminating welding or soldering.

Various further and more specific advantages and features will clearlyappear from the detailed description given below taken in connectionwith the accompanying drawing which forms part of this specification andillustrates merely -by way of example one embodiment of the device ofthe invention. In the following description and in the claims, partswill be identified by specific names for convenience, but such names areintended to be as generic in their application to similar parts as theart will permit. Like reference characters denote like parts in theseveral figures of the drawing, in which:

FIG. 1 shows a heating element coil end having a bentoff connecting pin;

FIG. 2 shows a radially taken partial section of the hotplate,illustrating the first step of placing the heating element coil in thehotplate body;

FIG. 3 shows the same radially taken partial section of the hotplate, asshown in FIG. 2, illustrating the loose filling of the insulatingcompound material over the heating element coils;

FIG. 4 shows the same' radially taken partial section of the hotplate asshown in FIG. 3, illustrating the pressing and compacting of theinsulating compound material;

FIG. 5 shows the same radially taken partial section of the hotplate asshown in FIG. 4, after the pressing of the insulating compound m-aterialhas been finished;

FIG. 6 shows a partial section of a hotplate having three heatingelements;

FIG. 7 shows a circuit Vdiagram of the heating elements of t-he hotplateillustrated in FIG. 6;

FIG. 8 shows a connecting pin soldered or welded a heating element coilend;

FIG. 9 shows a heating element coil end, straightened out over a shortlength, having a tu-bular connecting pin fastened to same; and i FIG. 10shows a heating element coil end, straightened out over ashort length,having a sheet metal strip rolled on said short length and pressed ontosame;

Referring now inv more detail to the drawing illustrating a preferredembodiment by which the invention maybe realized, there is shown in FIG.6 an electrichotplate body 10 which may be made of cast iron -or of anysuitable metal having a conventionally known recessed unheated centerportion 11 having a center screw bolt 12 for mounting of same in -anelectric cooking range (not shown in the drawing) and having heatedannular portion for receiving the heating element coils 14 embedded ininsulating compound material 16 and 17 in grooves 13.I A short, rigidconnecting part 15, shaped as a pin, is attached to each end of everyheating element coil 14, as shown in FIG. l, and as illustrated in anenlarged scale in FIGS. 8 to lOshowing various modes of fastening. Theconnecting parts have bent-off ends 15. y

The. straight length, measured from the end o the coil, amounts to 10-15mm. The bent-offends 15 are dimensioned in such manner that theyprotrude approximately 7 mm. over the .finally pressed insulatingcompound materi al on the underside of the plate body.

The assembling of the heating element coils 14 is performed as follows:

The rst step is to place the heating element coils 14 having theconnecting parts 15 into the grooves 13 of the hotplate Ibody 11i,turned upside down, after said grooves 13 had `been lined with apressed-in layer 16 of insulating material (FIG. 2). The bent-off ends15 of the connecting parts 15 of the inserted heating element coils 14extend upwardly beyond the grooves 13. Hereafter the insulating compoundmaterial 17 which is to be pressed into the grooves 13 is loosely pouredover the grooves and the surface of the material is evened smoothly. Theupright ends 15 of the connecting parts 15 are made so long that theyare entirely covered by the loosely poured and smoothly evened layer 17of the insulating compound material when'the dosage of the amount ofthis material has just been made right. The ends 15 of the connectingparts 15 will emerge from the insulating compound material aftercompressing the layer 17 of the insulating compound material by a diepress head 18 (FIG. 4). They enter during this process step intocavities 19 of the die press head 18. The ends 15 of the connectingparts 15 protrude approximately 7 mm. over the finally pressed layer 17of the insulating compound material, as shown in FIG. 5.

into

Conductor pieces 20 may -be welded or soldered to the ends 15 of theconnecting parts 15, which protrude over the surface of the layer 17 ofthe insulating compound material. These conductor pieces 20 are led in aconventional manner t-hrough slots of an insulating member 21 which isinserted into the cover shell 22 which is located underneath theAhotplate 1t) `and which is fastened there by the center screw bolt 12..rI`he conductor pieces 20 may be led to a terminal for the power line(not shown in the drawing) which is fastened in the conventional mannerto the underside of the hotplate. However, they also may `be led to theoutside of the insulating member 21, shaped as at bar plugs. -f

FIG. 6 shows a hotplatev having three heating elements N1, N2 and N3`which are connected with four terminal elements designated by thenumerals 1, 2, 3, 4 inthe circuit diagram, FIG. 7, lby Way of conductorpieces 20 which are welded or soldered to the connecting parts 15 ofthese heating elements. The ends of heating elements are schematicallyindicated in the insulating compound material 17.

FIGS. 8 to l() illustrate various possibilities of attaching connectingparts 15 to the ends of the heating element coils 14. According to FIG.8 a solid metal pin havingan outside diameter correspond-ing to theinside diameter of the coil, is inserted into the coil and is weldedtherewith at 25. In both alternatives, shown in FIGS. 9 and 1U, a shortend 26 of the heating element coil 14, corresponding to the length ofthe connecting part 15. According to FIG. 9, a small tube representingthe pin, having a length of approximately l5 mm. and anoutsidediameterof approximately 1.2 mm., is pushed on the straightened end 26of the heating element coil 14 andis pressed or crimped togetherwith thewire 2.6 at the point 28. In FIG. l0 is shown that the connecting part15 is formed by a sheet metal strip folded to a U- shape, which isrolled about the wire end 26 inserted into it, *forming a sort ofsleeve, which is pressed together with the wire end 25 at the sameinstant.

The operation of bending oft .the connecting parts is preferablyperformed after the connection with the heating element coil wire endhas been made.

Obviously the connecting parts 15 also can be dimensioned in such mannerthat they do not protrude over the pressed insulating compound material.In this case, the connecting parts 15 do not have to be bent off. Theyrather may bel laid bare for welding or soldering contacting pieces bymachining away a corresponding portion of the insulation, for example,by using a milling tool. v

While the invention has been described and illustrated with respect to acertain preferred example which gives satisfactory results, it will beunderstood by those skilled in the art, after understanding theprinciple of the invention, that various other changes and modificationsmay be made without departing from the spirit and scope of the inventionand it is intended therefore in the appended claims to cover all suchchanges and modifications.

'I claim:

1. An electric hotplate for an electric cooking range or the like,comprising a plate body having grooves in the underside thereof, heatingele-ments .embedded in an insulating compound material adapted to bereceived in said grooves, said heating elements consisting of wire coilshaving terminal windings, short connecting parts attached directly tothe ends of said heating elements, said connecting parts consisting ofsolid pins being pushed into said terminal windings of said wire coilsand being secured thereto, each one of said connecting parts having abent-off end portion projecting from said insulating compound material,a second insulating member underneath said plate body, a cover shell ofsaid plate body fitting over said second insulating member, andnoninsulated conductor pieces secured to said bent-olf end 5 portions,said conductor pieces passing through said second insulating memberfitted into said cover shell of said plate body, said conductor piecesproviding for connections with power lines of an electric currentsource.

2. An electric hotplate according to claim 1, and each one of saidconnecting parts being substantially l0 to 15 mm. long.

3. An electric hotplate according to claim 2, and each one of saidbent-off portions projecting from said insulating compound material bysubstantially 7 mm.

4. An electric hotplate according to claim 1, and said connecting partsconsisting of tubes being pushed over straightened end portions of saidWire coils and being squeezed therearound.

5. An electric hotplate according to claim 1, and said 15 6 6. Anelectric hotplate according to claim 1, and having a terminal barattached underneath said hotplate at a distance from said heatingelements embedded in said grooves, and said conductor pieces passingthrough said second insulating member fitted in said cover shell andbeing connected with said terminal bar.

References Cited by the Examiner UNITED STATES PATENTS 2,042,203 5/1936Baker 219-457 2,354,808 8/1944 Ganci 338-253 FOREIGN PATENTS 199,949 9/193 8 Switzerland.

RICHARD M, WOOD, Primary Examiner. L. H. BENDER, Assistant Examiner.

1. AN ELECTRIC HOTPLATE FOR AN ELECTRIC COOKING RANGE OR THE LIKE,COMPRISING A PLATE BODY HAVING GROOVES IN THE UNDERSIDE THEREOF, HEATINGELEMENTS EMBEDDED IN AN INSULATING COMPOUND MATERIAL ADAPTED TO BERECEIVED IN SAID GROOVES, SAID HEATING ELEMENTS CONSISTING OF WIRE COILSHAVING TERMINAL WINDINGS, SHORT CONNECTING PARTS ATTACHED DIRECTLY TOTHE ENDS OF SAID HEATING ELEMENTS, SAID CONNECTING PARTS CONSISTING OFSOLID PINS BEING PUSHED INTO SAID TERMINAL WINDINGS OF SAID WIRE COILSAND BEING SECURED THERETO, EACH ONE OF SAID CONNECTING PARTS HAVING ABEND-OFF END PORTION PROJECTING FROM SAID INSULATING COMPOUND MATERIAL,A SECOND INSULATING MEMBER UNDERNEATH SAID PLATE BODY, A COVER SHELL OFSAID PLATE BODY FITTING OVER SAID SECOND INSULATING MEMBER, ANDNONINSULATED CONDUCTOR PIECES SECURED TO SAID BENT-OFF END PORTIONS,SAID CONDUCTOR PIECES PASSING THROUGH SAID SECOND INSULATING MEMBERFITTED INTO SAID COVER SHELL OF SAID PLATE BODY, SAID CONDUCTOR PIECESPROVIDING FOR CONNECTIONS WITH POWER LINES OF AN ELECTRIC CURRENTSOURCE.